The surface plot is fairly benign looking. The surface dewpoints are in the low 60s with very little in the way of a boundary to focus lifting. The NAM and GFS had very innocuous precipitation forecasts. The NAM predicted a little more than .50 inch just to the southwest of STL. The GFS had .50 inch or more, mostly in Illinois. Most forecasters would probably forecast some precipitation with the MCV and might beef up the models some.

Convection started to develop at around 02 UTC near the center of the circulation. Remember the NAM and GFS had some convective precipitation forecast in this general area but did not predict any amounts greater than 1.00 inch. Often the convection associated with MCVs produce their rainfall maximum at night.

The 06 hr forecast sounding from the 00 UTC RUC indicated that the CAPE would be around 1000 J/kg at Union MO and that there would be a potent low level jet of 45 kts (see below).

0600 UTC meso-surface analysis (from Glass et al. 2001)

The RUC sounding above shows a number of factors that suggest that any MCS that forms and persists from 0215 UTC to 0600 UTC will probably produce high rainfall rates. Which of the following would support such a forecast?

Convection continued to develop along the western edge of the boundary through around 1200 UTC. The southwest winds kept the moisture feeding into the boundary and new cells kept forming even as the old cells move east and weakened. This is a case where the MCV helped generate convection but then the MCV kept moving eastward.

The observed rainfall rates at Union Missouri were in the 2-3 inch per hour range from 0630 UTC to 1030 UTC. If you were a forecasting in St Louis looking at a time cross section showing reflectivity, there was a big clue that heavy rainfall might be occurring, the high reflectivity area on the cross section was located below the freezing level. Therefore, it was unlikely that hail was causing the high reflectivity or that the NEXRAD algorithms would be overestimated rainfall rates.

16 inched of rain fell just west of union which received more than 12. Not all MCVs produce such copious rainfall, in fact many dissipate without producing a second round of convection.

MCVs are more likely to form and persist in regions of weak mid to upper level shear. A highly sheared environment is not favorable for their development or maintenance. If the surrounding airmass is moist and unstable there is a good possibility that a new round of convection will develop, such systems are especially dangerous if a low level jet develops and feeds moisture into upstream flank (usually southwestern flank) of the developing MCS (Trier and Davis 2002).